Multilayer laminates comprising an aluminum foil or an aluminum metallized substrate and one or more thermoplastic films have been known for a long time.
The advantages of aluminum are barrier to gasses and light, and a typical agreeable glossy metallic appearance.
However, it is impossible to use aluminum foil or aluminum metallized substrates in shrinkable structures. In turn, thermoformation is possible only to a very limited extent exclusively when the metallized substrate is a thermoplastic resin.
in addition, packages made from multilayer laminates comprising an aluminum foil or an aluminum metallized substrate cannot be used in microwave ovens, owing to electrostatic discharges and electric arc formation in the oven.
Another drawback is the difficulty to maintain a high level of barrier due to the formation of pin-holes particularly when the package is submitted to abuse during handling and transportation.
A further drawback of aluminum foil is that there is a concern about the recyclability and the incineration of the structures containing it.
DE-A-4 137 139 discloses a non-shrinkable and non-thermoformable thermoplastic film comprising from 0.1 to 6% by weight of a metal powder selected from the group consisting of aluminum, magnesium, zinc and manganese. This film is used in the manufacture of a laminate comprising an aluminum foil and has the aim of increasing the resistance of said aluminum foil to aggressive agents.
U.S. Pat. No. 4,985,300 describes a heat resistant microwave transparent base film which is first oriented and then coated with a layer of microwave susceptor material. The microwave susceptor material which is applied in a substantially continuous layer by means of conventional coating methods such as vacuum deposition and solution coating, should not be so thick to completely prevent penetration of microwave energy to the interior of the packaged food but should be used in amount sufficient to cause the film to heat under microwave cooking conditions to provide browing and crisping of the surface while providing a degree of microwave shielding for the interior of the food to avoid its overcooking. The method of applying the microwave coating must be one which does not expose the heat shrinkable film to high temperatures; otherwise the film will shrink during processing.
The Applicants are not aware of any heat shrinkable or thermoformable, substantially microwave-transparent multilayer film with metal-like appearance.